The invention relates generally to a system and method of terminating tubing that extends through a member. In particular, the invention relates to a system and method for terminating tubing that extends through a wellhead component.
A downhole safety valve is a safety feature used in oil and gas wells. As its name implies, a downhole safety valve is located in a well at a point below the surface of the ground. The purpose of a downhole safety valve is to prevent an uncontrollable release of fluids from an underground reservoir in the event of damage to the surface components of a well. For example, the surface components of a well may be destroyed or damaged by the wind and waves produced by a hurricane. In such a scenario, the reservoir fluids could flow to the surface and be released into the environment if a downhole safety valve was not in service. Downhole safety valves commonly are unidirectional valves that are oriented in the well's production tubing such that a flow of wellbore fluids upward from an oil or gas reservoir causes the downhole safety valve to close, preventing the wellbore fluids from reaching the surface.
Typically, hydraulic pressure applied through tubing, referred to as a control line, is used to control downhole safety valves. When sufficient hydraulic pressure is applied down the control line, the downhole safety valve is forced open. This enables wellbore fluid to flow up and out of the well through the production tubing. However, if the hydraulic pressure in the control line is lost, a spring within the downhole safety valve will close the downhole safety valve, thereby preventing wellbore fluid from flowing out of the well. Typically, the pressure used to operate the downhole safety valve is greater than the pressure of the wellbore fluids. For example, if the wellbore fluids were being produced at a pressure of 15,000 psi, the control line for the downhole safety valve may be set to provide a pressure of 17,000 psi to open the downhole safety valve.
The control line typically is directed upward from the downhole safety valve through the casing of the well. During the stage of well development when a blowout preventer (BOP) is installed over the well, the control line is routed through the BOP to a well control panel. Later, when the BOP is no longer necessary, the BOP is removed and the control line is re-routed through a port of another wellhead component. The control line is terminated at a termination connection that is threaded directly into the port of the wellhead component. A seating surface is machined into the wellhead component to enable a seal to be formed between the control line and the port to prevent wellbore fluids from leaking from the wellhead component via the annulus that surrounds the control line.
However, this method for terminating a control line in a wellhead component is problematic. Wellhead components may be quite large and bulky, thereby making machining operations on them difficult and time consuming. Forming a seating surface, such as a conical section, on a surface of a wellhead component may be particularly difficult and time consuming. In addition, when the seal is exposed to a high pressure, such as 15,000 psi, the port through the wellhead component may have to be very small relative to the diameter of the control line to enable the annulus of the control line to be sealed using a sealing member and the seating surface of the wellhead component. This adds an additional level of difficulty to the process of machining the port through the wellhead component. For example, in this type of operation, the diameter of the port may have to be as small as 5/16 of an inch for a ¼ inch control line. Machining a 5/16 inch hole in a large, heavy, bulky object, such as a wellhead component, may be particularly difficult and time consuming.
Therefore, a more efficient technique is desired for terminating tubing extending through wellhead equipment. In particular, a technique is desired that would enable downhole tubing to be terminated at a wellhead component quickly and easily without difficult machining operations.